Nonalcoholic fatty-liver disease (NAFLD) is one of the most prevalent liver diseases in western countries. The full pathophysiology of NAFLD is still unknown. Both obesity and insulin resistance are considered to play a strong role in the disease process. Indeed, the rising rates of obesity and diabetes mellitus correlate with the increasing incidence of NAFLD, which is the hepatic and early manifestation of metabolic syndrome. Estimates suggest that about 20% to 30% of adults in developed countries have excess fat accumulation in the liver, 50% among people with diabetes, and about 80% in the obese and morbidly obese individuals.
Non-alcoholic steatohepatitis (NASH) is the most severe form of NAFLD, and can progress to more severe forms of liver disease, including fibrosis progression, cirrhosis, and even hepatocellular carcinoma.
The disease begins with the aberrant accumulation of triglycerides in the liver, resulting in simple steatosis; most patients who develop steatosis are stable and further disease does not develop. However, some individuals progress to NASH, the severe form of NAFLD. In NASH, up to 20% of patients' progress into cirrhosis.
The normal liver is composed of hepatocytes and non-parenchymal cells, which include kupffer cells, sinusoidal endothelial cells, and myofibroblasts known as Hepatic Stellate Cells (HSCs). HSCs are considered to be involved in the pathogenesis of liver fibrosis from any etiology, including NASH-related hepatic fibrosis. In normal liver, HSCs are described as being in a quiescent state and serve to store retinoids (vitamin A). Quiescent stellate cells represent 5-8% of the total number of liver cells. When the liver is damaged, HSCs can change into an activated state characterized by contractions, loss of lipid droplets and enhanced of proliferation, cell migration as well as cellular adhesion. HSCs are also unequivocally the main cells involved in the production of excessive ECM seen in liver fibrosis. Since activated HSCs themselves secrete inflammatory chemokines, a vicious cycle is formed, whereby fibrogenic and inflammatory cells stimulate each other and perpetuate a process of liver damage and repair.
Natural killer (NK) cells are a key component of the innate immune system, and play a critical role in the early stages of the immune response against tumor cells, as well as those infected by viral and microbial pathogens.
In humans, two NK-cell subsets have been characterized according to the cell-surface density of CD56 and expression of CD16. CD56dimCD16bright NK cells (hereinafter CD56dim) compose approximately 90% of circulating NK cells; CD56brightCD16dim NK cells (hereinafter CD56bright) constitute approximately 10%. CD56bright NK cells proliferate and produce interferon in response to stimulation with interleukin-12 (IL-12), whereas CD56dim NK cells are more cytolytic and produce significant amounts of cytokine when their activating receptors are engaged.
In a paper published by some of the inventors it was found that, as opposed to CD8 immune cells, NK cells have anti-fibrotic activity through stimulation of HSC killing. (Melhhem et al., J. Hepatology; 2006; 45: 60-71). It has also been reported that the function of NK cells decreases when the liver disease progresses into cirrhosis, suggesting that attenuating NK function is a prerequisite for the progression of the disease (Seki et al.; Clin Dev Immunol.; 2011; Article ID 868345).
Human neuroligin-4 (NLG4, NLGn4, NLGn4X) encodes a member of a family of neuronal cell surface proteins called the Neuroligins. FIG. 1 illustrates the neuroligins and their interactions. Members of this family may act as splice site-specific ligands for beta-neurexins and may be involved in the formation and remodeling of central nervous system synapses. The encoded protein interacts with discs, large (Drosophila) homolog 4 (DLG4). Mutations in this gene have been associated with autism and Asperger syndrome. NLGn4 is also detected with high levels of expression in heart and lower in liver, skeletal muscle and pancreas.
The clinical implications of NAFLD are derived mostly from its potential to progress to cirrhosis and liver failure. There is an unmet medical for compositions and methods for treating NAFLD and preventing the progression to cirrhosis. Nowhere in the art has it been suggested that disease progression of NAFLD can be modulated by attenuating NLGn4 expression and thereby NK cell activity.